Method for measuring the duration of inhibition of angiotensin I-converting enzyme in vivo.

The spontaneously hypertensive rat, either pithed or anesthetized with urethane, responds to intravenous injections of angiotensin I (A1) and angiotensin II (AII) with pressor responses. These responses vary with time, but the ratio of the responses to AI and AII is constant throughout 4.5 hr. This criterion was used to determine the degree and the duration of effect of captopril. At low (30 micro g/kg iv) and high (3mg/kg iv) doses, it selectively reduces the pressor response to AI, so reducing the AI/AII ratio. The rate of recovery is initially rapid followed by a prolonged slower phase. The degree (maximum 65%) and the duration of inhibition are directly related to the dose of the inhibitor.